1. Field of the Invention
The present invention relates to a wide angle zoom lens.
2. Description of the Related Art
Numerous wide angle zoom lenses that can be used on imaging apparatuses equipped with a solid-state image sensing device such as a CCD, C-MOS, and the like have been proposed (for example, refer to Japanese Patent Laid-Open Publication Nos. 2012-194238, 2009-271165, and 2009-103790).
There is a growing need among web cameras, monitor cameras, video cameras, etc., for zoom lenses that can capture wide angle images with high sensitivity. To reduce crime and to record highly reliable evidence, in the field of surveillance cameras as well, there is a growing need for zoom lenses that have a simple configuration and that can capture bright wide-angle images in not only the visible light region but also in the near-infrared light region. Consequent to the increasingly smaller size of imaging apparatuses further size reductions are also demanded of zoom lenses.
Nonetheless, with convention technologies such as the optical systems disclosed in the patent documents above, a zoom lens satisfying recent needs has yet to be realized.
For example, the optical system disclosed in Japanese Patent Laid-Open Publication No. 2012-194238 has a wide angle focal length to telephoto focal length ratio (zoom ratio) on the order of 5 to 9 and can favorably correct variations in aberration during zooming. Nonetheless, with an F number on the order of 2.1 to 2.7, the optical system is a dark lens. The optical systems disclosed in Japanese Patent Laid-Open Publication Nos. 2009-271165, and 2009-103790 are respectively bright, having an F number on the order of 1.5 and also favorably correct variations in aberration during zooming. Nonetheless, the zoom ratio is small, on the order of 1.5. Thus, it is difficult to say that the optical systems disclosed in the patent documents above achieve reductions in the overall length of the optical system to an extent satisfying recent needs.